Open System Interconnection, developed by the ISO and the ITU-T, defines networking as seven layers. Control of data is passed from one layer to the next as the information works its way across the network - and each layer has its own set of protocols. As networking has evolved, devices such as switches have gradually worked their way up the stack, to the point where there are now Application Layer switches. The seven layers:
1. Physical Layer
2. DataLink
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer
Additional resources
OSI Protocols
Cisco overview.
